Fig. 2: Characterization of implantable piezoelectric ultrasound stimulator (ImPULS).

a The impedance and phase angle spectra of the ImPULS in air and water, showing the resonance frequency in both mediums. b Displacement of ImPULS in air and water mediums measured using laser Doppler vibrometer (LDV) at 4 V (p-p) when the inputs are a periodic chirp (bottom) and a sinusoidal signal (top). c Displacement of ImPULS as a function of input voltage (p-p) with inset showing two-dimensional (2-D) point scan of displacement indicating the lateral resolution of the beam of the device. Error bar represents the standard deviation in measurement, N = 3 devices. Data represents mean values ± SD. d Simulated acoustic pressure profile of the ImPULS showing a spherical pressure distribution. e Comparison of simulated and experimentally measured pressure using a fiber-optic hydrophone at different distances. Error bar represents the standard deviation in measurement, N = 3 devices. Data represents mean values ± SD in the x and y directions. f 2-D mapping of pressure generated by the ImPULS measured at z = 15 μm. Scale bar, 25 µm. g Microscopic image of the ImPULS taken each 24 h apart during the aging test (left), and normalized displacement of ImPULS before the start of the test and after 7 days. Scale bar, 100 µm. Error bar represents a standard deviation in measurement, N = 3 devices. Data is normalized to the displacement measured on day 0 per device. Day 8 data represents the mean displacement ± SD. (a.u. arbitrary units). h Temperature change in water medium when a continuous sinusoidal signal of 500 kHz at 20 V (p-p) applied to the ImPULS. Ultrasound was ‘off’ for 10 min, ‘on’ for 10 min and ‘off’ for 10 min. i 2-D mapping of temperature generated by the ImPULS measured at z = 15 μm. Scale bar, 25 µm.